In FIG. 1 is shown a conventional ejector, well known in the prior art. This pumping device has the advantage of extreme simplicity, there being no moving parts. The principle of operation is that the high energy primary fluid entering the ejector through primary fluid inlet conduit 2, passes through a supersonic nozzle 5, and emerges therefrom as a high speed jet. Upon exiting said supersonic nozzle, the primary jet entrains secondary fluid introduced through secondary fluid inlet conduit 3 into plenum 24 through the action of turbulent mixing between primary and secondary fluid. The mixing and subsequent diffusion is controlled by aerodynamic shroud 10 and the mixed flow is discharged from the ejector at mixed-fluid outlet conduit 4. The conventional ejector, as a result of its simplicity, finds application in numerous technologies. Nevertheless, it suffers from low efficiency as a result of the inherent irreversibility of the mechanism with which it operates: turbulent mixing. Despite a century of research on improving this device, its performance is limited by the nature of the physics of its operation.
Foa (U.S. Pat. No. 3,046,732) and Garris (U.S. Pat. No. 5,647,221) disclosed new types of ejectors which operate on a different principle from conventional ejectors: pressure-exchange. Due to the thermodynamically reversible nature of pressure-exchange, much higher efficiencies can be obtained, thereby making possible a new level of performance. Foa (U.S. Pat. No. 3,046,732) and Garris (U.S. Pat. No. 5,647,221) have discussed the fact that pressure-exchange is a different process which is thermodynamically reversible because it is based on the work of interface pressure forces as opposed to highly dissipative process of turbulent mixing. They further disclosed ejectors which utilize both the pressure-exchange mechanism in addition to the turbulent mixing mechanism.
A figure of merit on ejector performance is provided by comparing the performance of an ejector with the ideal turbo-machinery analog of an ejector. In the turbo-machinery analog, shown in FIG. 2; a turbine (expander) 83 directly drives a compressor 84 through its output shaft 85, said turbine being energized by a high pressure primary fluid which is introduced through inlet conduit 2, and the compressor taking suction through inlet conduit 3 from a source of relatively low energy secondary fluid which is to be energized, both compressor 84 and turbine 83 discharging into a common exit passage 4 (connection between turbine discharge and compressor discharge not shown.) If the processes occurring in the turbo-machinery are assumed to occur isentropically and thermodynamically reversibly, the adiabatic efficiency obtained is optimal. Since real conventional ejectors depend on irreversible processes, their adiabatic efficiencies are a small fraction of the turbo-machinery analog.
The concept of using turbo-machinery in place of ejectors to improve efficiency is known in the art. This is termed the “turbo-machinery analog”. Rice et al (U.S. Pat. No. 3,259,176) disclosed the use of the turbo-machinery analog in a refrigeration system which is equivalent to an ejector refrigeration system but with the ejector replaced by the turbo-machinery analog. However, the advantage of the conventional ejector is its simplicity. The conventional ejector has no moving parts, whereas, equivalent turbo-machinery requires a high precision product using advanced materials, and which is very costly. Utilizing the turbo-machinery analog in refrigeration applications would require very large and costly machinery if low density refrigerants were used. Furthermore, topping cycles utilizing the turbo-machinery analog would not be able to handle the high temperature working fluids better than standard turbo-machinery. Hence, for these applications, the turbo-machinery analog would not be adequate. An objective of the present invention is to provide an ejector which satisfies the need for high efficiency through the use of pressure-exchange, approaching the efficiency of the ideal turbo-machinery analog, yet which retains much of the simplicity of the conventional ejector.
Foa (U.S. Pat. No. 3,046,732) invented an ejector which utilized the benefits of pressure exchange through the use of rotating primary jets. He further showed how the rotating primary jets, when incorporated into a rotor, could be made self-actuating by means of canting the nozzles at an angle with respect to the azimuthal plane. Garris (U.S. Pat. No. 5,647,221) taught how when the working fluid was compressible, shock and expansion wave patterns could be used to advantage in effecting flow induction by pressure-exchange. Garris (U.S. Pat. No. 5,647,221) further taught how pressure-exchange ejectors might effectively be utilized in ejector refrigeration. While these prior art devices offer effective aerodynamic means to provide excellent use of pressure-exchange to affect flow induction, they are deficient in that they require a very high degree of precision in manufacturing to provide the level of sealing necessary while allowing the rotor to spin at the high angular velocities necessary to achieve effective pressure-exchange. Furthermore, in these prior-art pressure-exchange ejectors, the demands on the rotor thrust-bearing are very high due to the high internal supply pressure and the low external suction pressure occurring simultaneously with very high rotor angular velocities. This very demanding combination of requirements for sealing, high rotational speeds, and thrust bearing tend to substantially increase the cost of the device and reduce its potential service life. Garris (U.S. Pat. No. 6,138,456) taught how the sealing requirements implicit in the use of rotating nozzles can be eliminated while the thrust demands substantially alleviated by the use of a self-driven rotating vane ejector where the vanes have aerodynamic shapes consistent with supersonic flow. In the embodiments shown by Garris (U.S. Pat. No. 6,138,456), the vanes assumed the form of sharp edged wedges placed peripherally around the rotor and at an angle to the axial plane so as to enable the self-driving features. Garris further taught that the best mode was for the rotor to turn at its free-spinning speed; viz., the speed that occurs when there is no bearing friction and the flow paths of the fluid particles emanating from the primary flow are in the axial plane in the laboratory frame of reference. Garris further taught that the presence of supersonic flow structure such as shock waves and expansion fans does not prevent the exploitation of the reversible work of interface pressure forces provided in the pressure exchange process. However, although computer simulations and experimental results on the wedge-type vaned rotor did succeed in showing the benefits of pressure exchange, the wedge design of the rotor vanes may be too thin to provide a rotating periodic flow structure to optimally utilize pressure exchange. An objective of the present invention to obtain a pressure exchange ejector which provides improved performance in the transfer of momentum and energy from the primary to the secondary fluid by providing a more robust primary-secondary interface. It is therefore the principal objective of the present invention to provide an ejector which effectively exploits pressure-exchange for flow induction, yet is less demanding with regard to sealing, thrust management, and high rotational speeds. Another objective of the present invention is to provide a pressure-exchange ejector which is simple and economical to manufacture. Still another objective of the present invention is to provide a pressure-exchange ejector which is suitable for compressor applications such as ejector refrigeration, fuel cell pressurization, water desalinization, applications and power generation topping-cycle use for both gas turbines and Rankine cycle systems. While pressure-exchange ejectors can find considerable use in gas and vapor compression applications, and in that connection, the benefits of supersonic gas flow can be effectively utilized, pressure-exchange can also be effectively utilized in incompressible fluids such as liquids for pumping applications such as water-jet marine propulsion. It is also an object of this invention to provide an ejector for use in liquid pumping applications such as water jet marine propulsion.